Characterization of Mononuclear and Dinuclear Germylplatinum Complexes and Ge−Ge Bond Formation at the Platinum Center

Abstract

The reaction of the zerovalent platinum complex [Pt(PPh3)2(η2-C2H4)] (1) with the germanium trihydride GeH3Mes (Mes = 2,4,6-trimethylphenyl) produced various germylplatinum complexes by control of the molar ratio. When complex 1 reacted with GeH3Mes in a molar ratio of 1:1, dimerization of the platinum unit occurred at −30 °C to afford the unsymmetrical diplatinum complex [Pt2(PPh3)3(μ-GeH2Mes)2] (2) and the symmetrical diplatinum complex [Pt(PPh3)(μ-GeH2Mes)]2 (3), for which the 1H NMR spectrum indicated a mixture of cis/trans-isomers in a ratio of 2:3. When a toluene solution of 2 increased in temperature from −20 °C to room temperature, liberation of a PPh3 group occurred at the Pt(PPh3)2 site, followed by rotation of the bridging germyl group to form a mixture of cis/trans-3. Otherwise, treatment of 1 with GeH3Mes at a molar ratio of 1:2 afforded the bis(germyl)platinum complex [Pt(PPh3)2(GeH2Mes)2] (4) at −30 °C, and then 4 converted to the digermanylplatinum hydride [Pt(PPh3)2(H)(GeHMesGeH2Mes)] (5) at room temperature in toluene. The conversion rate obeyed a first-order rate law, and the activation parameters ΔH⧧ and ΔS⧧ were calculated at 20(2) kcal mol−1 and −7(8) cal K−1 mol−1, respectively. These results suggest that in later transition metal platinum complexes, Ge−Ge bond formation is carried out by intramolecular germyl migration.